In its position of application, the metal gasket will be between a sealing surface of the receiving portion of the pipe and a sealing surface of an end portion of a further pipe.
When so-called hammer unions (also called: wing unions, hammer lugs, Weco unions) are used as fireproof unions, metal gaskets must be used. Gaskets made entirely or partly from rubber or a synthetic material are not usable because of their relatively poor temperature resistance.
Metal gaskets are used in connections in blowout preventers (BOPs) and must resist both fire and high pressures. The metal gaskets that are used in blowout preventers today are used under dispensation because they do not satisfy the safety requirements that apply.
As is known, metal gaskets are relatively rigid and it is a problem, especially when the hammer union is mounted vertically, that the gasket falls out of the union before the opposite union part, the end portion of the further pipe, that is, has been mounted.
Hammer unions are a relatively old product that is available with gaskets in a number of designs and materials. However, none of the known designs solves the problem in question.